This invention relates generally to the installation in a flow line of an instrument such as a flowmeter whose cylindrical body has a flow conduit therein in a manner centering the cylindrical body with respect to the line pipes, and more particularly to camming devices to facilitate such centering.
Though the invention is of particular value in connection with the installation of a flangeless electromagnetic flowmeter in a flow line, it is also applicable to other instruments such as valves and turbine meters which have cylindrical bodies and which suffer from similar centering problems. Hence while the invention will be described herein in the context of a flangeless electromagnetic flowmeter, it is to be understood that the invention is not limited to this application.
Typical of commercially-available electromagnetic flowmeters adapted to measure the volumetric flow rates of fluids such as acids, sewage and slurries which present difficult handling problems is the Fischer and Porter Co. (Warminster, Pa.) Model 10 D 1430 meter. Because a flowmeter of this type has an obstructionless flow conduit, it can be used to meter fluids without regard to heterogeneous consistency. The model 10 D 1430 flowmeter includes a carbon steel pipe spool flanged at both ends, the spool serving as the meter body.
In installing a standard flanged flowmeter in a flow line, the meter must be interposed between upstream and downstream pipes each having an end flange. For this purpose, the mounting flanges on the flowmeter are provided with a circle of bolt holes that register with the bolt holes in the end flange of the line pipes. The installation is made by bolting the end flanges of the upstream and downstream pipes to the corresponding mounting flanges of the meter. To prevent leakage of fluid, gaskets are sandwiched between the bolted flanges. Because of the matching bolt holes in the meter and the flanges, the installed meter is centered with respect to the line pipes.
Standard flanged magnetic flowmeters are relatively large, heavy and expensive. Compact flowmeters are now known which are of much shorter length and are flangeless, one such meter being disclosed in the Schmoock U.S. Pat. No. 4,181,018. A meter of this type is designed for compression mounting between the end flanges of the upstream and downstream line pipes, the bolts in this instance bridging the pipe flanges to compress and encage the flowmeter.
The term "flangeless," as used herein, is intended to cover a meter whose cylindrical body is entirely without flanges or is provided with small end flanges that lack bolt holes and serve only to press gaskets against the flanges of the line pipes to prevent leakage at these joints.
In a flangeless meter in which the meter compressed between the end flanges of the line pipes is encaged within a circular array of clamping bolts bridging these flanges, the bolts perform no centering action as in the case of flanged meters in which the bolts pass through complementary holes in the meter flanges. As a consequence, one is faced with the problem of misalignment between the flow conduit of the meter and the line pipes.
The performance of a flowmeter, and to a lesser extent that of the gaskets used to provide a seal between the ends of the meter and the line pipes, depends on correct meter centering. An improperly centered meter, because it is misaligned with the flow line, will cause changes in the hydraulic profile of the fluid conveyed by the line and give rise to local turbulence as the fluid passes through the meter. As a result, there are errors in meter readings.
One possible solution to this problem is to mount a template or dummy flange on the body of the meter, this dummy flange containing several sets of bolt hole patterns, the holes in the sets being interspersed. These sets are appropriate for a range of possible pipe flange bolt hole patterns. Thus when the flangeless meter is interposed between the flanged ends of upstream and downstream pipes, the dummy flange is then indexed until one of the hole sets is in registration with the existing bolt hole pattern in the pipe flanges. The bolts which bridge the pipe flanges then pass through the holes in the dummy flange and thereby center the meter.
However, a dummy flange represents an inadequate solution to the centering problem, for a flange of this type can only accommodate a limited number of bolt hole patterns, and this number is well below the number of possible bolt hole patterns encountered in existing flanged pipe lines. Thus in the United States, there are ANSI class 150 lb., 300 lb. and 600 lb. sizes among others, and there are equivalent international DIN and BS flange sizes, each having a distinct bolt hole pattern.
For example, while a flangeless flowmeter whose flow conduit has a 3-inch diameter is intended to be interposed in a pipe line having a like internal diameter, the installer at different installation sites is likely to be faced with different flange sizes. Centering then becomes a difficult problem for which there is no obvious solution.
Another factor which makes centering a problem, even with a dummy flange or centering template is the clearances which must be allowed between the clamping bolts and pipe flanges so that the flowmeter can always be assembled in the line. For this reason, the typical circle of bolt holes in a pipe flange is provided with bolt holes that are somewhat larger than the bolt dimension, thereby allowing some degree of play. This creates an uncertainty of location that is particularly bothersome on small flowmeters where the percentage of this uncertainty is high relative to the meter size.